Study of Pitting Corrosion Inhibition of Mild Steel by Nitrite in Concrete Pore Solution by Polarization and Zero Resistance Ammetery (ZRA) Techniques (RESEARCH NOTE)

A research on the corrosion inhibition of mild steel pitting corrosion in concrete pore solution by sodium nitrite was carried out by employing potentiodynamic, potentiostatic polarization and zero resistance ammetery (ZRA) techniques. Passivity breakdown potential was decreased from the transpassive potential of 700 mV at the absence of chloride to a value of -50 mV when just 0.01M NaCl was added to the test solution and further a decrease to -350 mV was recorded when the concentration of chloride was increased to 0.5M. Addition of NaNO2 into the saturated Ca(OH)2 solution containing 0.5M NaCl considerably shifted the pitting potential towards noble values. Similar results of inhibitive effect of nitrite were obtained from couple potential and current measurement between two nominal identical electrodes through ZRA establishment. In the test solution containing NaNO2, continuous increasing of the corrosion potential towards noble values and simultaneous decrease in couple current density towards zero proved the stability and improvement of the passive film. Whereas, continuous decrease in couple potential accompanied with sharp increase in couple current density with a stable value of 3µA/cm2 at the absence of NaNO2 demonstrated the occurrence of pitting corrosion.